Phase Separation Dynamics of Polymer Blend Films Containing Polymer-Grafted Nanoparticles

Polymer blends containing nanoparticles (NP) are important in advanced technologies including opto-electronic and biosensor devices. Upon adding methyl-terminated silica NP's [22nm (NP$_{A})$] at dilute concentrations, PMMA:SAN (50:50) films (650nm) undergo early, intermediate and late stages of morphology development, similar to a PMMA:SAN film (Wang {\&} Composto, JCP (2000)). NP's partition into the PMMA-rich phase, and slow down the kinetics of domain growth. This result is consistent with a coalescence model that predicts $\xi \quad \sim $ (1 / $\eta )^{1/3}$ t$^{1/3}$, where $\xi $ and $\eta $ are the correlation length and PMMA viscosity, respectively (Chung \textit{et al}., EPL (2004)). Although the bulk $\eta $ agrees with this model, a microscopic understanding of the phase separation mechanism requires knowledge of polymer-NP and NP-NP interactions. To address this issue, well-characterized silica NP's (15 nm) with densely grafted PMMA [M$_{w}$ = 1.8K (NP$_{B})$ and 21K (NP$_{C})$] are employed as non-interacting fillers in the PMMA-rich phase. The impact of PMMA-grafted NP on the phase separation dynamics in films, as well as the rheology of PMMA/NP composites, is investigated. Specifically, phase separation was slowest for NP$_{B}$ relative to films containing NP$_{A}$ and NP$_{C}$. These studies show that wetting and domain coarsening in polymer blend films can be controlled by the judicial addition of surface modified NP.